1998 RM125 CYLINDER WITH SPACER UNDER TO LIFT CYLINDER

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I JUST PICKED UP A 1998 RM125 MY QUESTION IS WHY WOULD IT HAVE SOME SORT OF A SPACER BLOCK UNDER THE BOTTOM OF THE CYLINDER TO RAISE IT. THE CRANKSHAFT THAT IS IN IT MUST HAVE A LONGER ROD BECAUSE THE PISTON COMES TO THE TOP JUST AS IT IS SUPPOSED TO. HAS ANYONE EVER SEEN THIS DONE AND WHAT WOULD BE THE ADVANTAGE TO THIS MODIFICATION. ALSO WOULD YOU USE THE SAME OR AND TIMING AS IF IT WERE A STOCK SETUP. THIS IS A NEW ONE ON ME. I DID NOTICE THAT THAT YEAR DID HAVE DIFFERENT CYLINDERS AND CRANKSHAFTS DEPENDINGON WHAT LETTER MODEL YOUR ENGINE WAS. THE ONLY THING I CAN THINK OF IS MAYBE ONE OF THE MODELS IN THAT YEAR HAD A LONGER STROKE CRANKSHAFT. ANYONE WITH ANY INFORMATION ON THIS I WOULD LOVE TO HEAR FROM YOU. I AM MORE CURIOUS THAN ANYTHING. I HAVE LOOKED TO SE IF ANYONE MADE LIKE A STROKER KIT FOR THIS YEAR BIKE BUT I SEE NOTHING OF THE SORT. FRAME # JS1RF15C9W2100488 ENGINE # F114 147954 CYLINDER # 6GD0 I ALSO HAVE ANOTHER CYLINDER THAT CAME WITH IT # 8M1E THIS ONE HAS A CYLINDER LINER WITH IT TO BE INSTALLED AS THE CYLINDER HAS BAD GOUGES. THANK YOU HOPE TO HEAR FROM SOMEONE WHO KNOWS ALOT MORE THAN ME ON THIS ONE.

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Sounds like someones custom mods, reasons being more tourqe at all rpm ranges without increasing the displacement. My guess is the porting on that cylinder would be raised aswell, aswell as a custom head.. i could be wrong though. If yoir planning to rebuild it id personally go complete stock as it might be pretty expensive to have a crank made around a longer conrod.

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THE CRANKSHAFT IS ALREADY DONE AND IN THE BIKE SO MAYBE I WILL JUST TRY IT AND SEE WHAT IT DOES. THE IGNITION TIMING HOPEFULLY WILL STAY AT STOCK SETTINGS. IF I GO BACK TO STOCK I WOULD HAVE TO GET A STOCK CRANKSHAFT. THANK YOU FOR YOUR REPLY.

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I would try contacting the guy that you got it from and see if he can give you some history on the bike, maybe even do a title search and see if the DMV can tell you who the original owner was. Also, see if there's any custom hand ground markings or lettering on the cylinder that might give away who did the work. Adding a spacer under the cylinder opens up the possibilities as to the number of possible things that could be done to the engine and cylinder. A longer rod is the #1 guess, but it's also possible that the cylinder was raised and then the top shaved off to change the port timing.

How thick is the spacer and do you have to run race gas?

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THE SPACER IS PROBABLY 3/4 TO 1 THICK DONT KNOW ABOUT THE GAS I HAVE NOT HAD IT RUNNING YET. WOULD THE IGNITION TIMING STAY THE SAME OR WOULD I HAVE TO MODDIFY THE PLATE SO IT CAND BE ADVANCED OR RETARDED.

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I think the bike could have a "stroker" crank installed in it. This would require a greater cylinder length and would result in greater displacement and torque.

Displacement is the size of the bore, not the length of the stroke... longer conrods are put in bikes to increase tourqe without increasing the displacement so it it can still be raced in its respective class.

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Displacement is the size of the bore, not the length of the stroke... longer conrods are put in bikes to increase tourqe without increasing the displacement so it it can still be raced in its respective class.

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THE CRANKSHAFT IS ALREADY DONE AND IN THE BIKE SO MAYBE I WILL JUST TRY IT AND SEE WHAT IT DOES. THE IGNITION TIMING HOPEFULLY WILL STAY AT STOCK SETTINGS. IF I GO BACK TO STOCK I WOULD HAVE TO GET A STOCK CRANKSHAFT. THANK YOU FOR YOUR REPLY.

Did you ever get your bike back together? If not, try posting some pictures of the cylinder and the spacer. As for the timing, just pull the timing cover off and check the marks, then you'll know if it's been messed with.

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I had a yz 250 from that era that had the same thing. Back then it was called the "long rod kit". It was a spacer, two base gaskets and a longer rod(5mm i think) and some other stuff needed for the power valve. It increased bottom end hit on the 95 yz 250 i had. I heard suzuki did a similar thing with the last gen of the rm125 adjusting the rod length/ratio to be more like the kits were. It alters a handful of things and depending on the motor you may or may not even feel the different. If you opt to not use the spacer you need to go back to a stock rod length and make sure all the associated power valve linkages/etc are ok.